This invention relates to a transformer and a method of manufacturing the transformer. The method comprises the steps of providing a coil bobbin having a first and second end on which are situated respectively a first flange and a second flange, said flanges defining a winding space on the coil bobbin, at least the first flange being provided with radially extending edge slots; winding a first coil in the winding space, said coil being formed from a wire conductor, the ends of which are led out via at least one of the edge slots; applying an electrically insulating foil over the first coil; and winding at least one second coil on the said foil.
A transformer of this kind is known, for example, from U.S. Pat. No. 4,449,111. The insulating foil serves for electrically separating the first and the second coils from each other. Special measures are needed to ensure that, near the flanges, the conductors of the first and the second coil do not come too close together since there would then be a danger that the creep path between the first and the second coil could become impermissibly short or even that a conductor of the second coil could slide over the edge of the foil and come into contact with the first coil. Such measures consist in the application of a separate coil bobbin consisting of two parts for the second coil, which coil bobbin is placed around the first coil, or in the application of a corrugated edge to the foil which is folded against the sides of the flanges directed towards the winding space, thereby ensuring a minimum distance between the first and the second coil. These solutions are however relatively expensive and offer little scope for modifying the design of the transformer, for example by changing the number of second coils.